Vaporizer

ABSTRACT

There is provided a vaporizer in which the path of a reaction tube can be kept long, and vaporization can be promoted evenly by radiation heat from a heater by agitating a carrier gas into which a source solution is dispersed in the direction crossing the passing direction of the gas, the agitation being made by a centrifugal force produced when the gas passes through the reaction tube. A carrier gas into which a source solution consisting of a liquid or powder is dispersed is supplied from the upstream side to a spiral reaction tube  103,  and the carrier gas into which the source solution is dispersed and which passes through the reaction tube  103  is vaporized by radiation heat from a heater  104.

TECHNICAL FIELD

The present invention relates to a vaporizer for vaporizing, byradiation heat from a heater, a carrier gas into which a source solutionis dispersed and which passes through a reaction tube.

BACKGROUND ART

Patent Document: Unexamined Japanese Patent Publication No. 2000-216150

In recent years, in the field of electronic device, as the circuitdensity increases, smaller size and higher performance of electronicdevice have further been demanded. For example, like SRAM (Static RandomAccess read write Memory) in which storage operation of information isperformed by a combination of transistors, EEPROM (Electrically Erasableand Programmable Read Only Memory), or DRAM (Dynamic Random AccessMemory) in which storage operation of information is performed by acombination of transistors and capacitors, not only the fulfillment offunction of electronic device achieved simply by a circuit configurationonly but also the fulfillment of function of device achieved byutilizing the characteristics of the material itself such as afunctional thin film has become advantageous.

Therefore, a dielectric material used for an electronic part is desiredto be made a thin film. One method for making such a material a thinfilm is the CVD process.

This CVD process has features of a film forming rate higher than that ofthe PVD process, sol-gel process, and other film forming methods, easymanufacture of multilayer thin film, and the like. Also, the MOCVDprocess is a CVD process in which a compound containing an organicsubstance is used as a raw material for forming a thin film, and hasadvantages of high safety, no mixture of halide in a film, and the like.

The material used for the MOCVD process is generally solid powder orliquid. In this process, the material is put in a vessel, and isgenerally heated at a reduced pressure and vaporized in a vaporizer, andthereafter is sent into a thin-film forming apparatus by a carrier gas.

FIG. 4 is a system block diagram of a vaporization system for the MOCVDprocess (refer to Patent Document 1).

In FIG. 4, reference numeral 10 denotes a supply section for supplying aplurality of source solutions etc. to a vaporizer 1.

The supply section 10 includes a gas cylinder 11 filled with a carriergas (for example, N₂ or Ar), an oxygen cylinder 12 filled with oxygen, awater storage tank 13 in which cooling water is stored, a plurality ofreservoirs 14 to 17 in which raw materials for ferroelectric thin film(for example, Sr(DPM)₂, Bi(C₆H₅)₃, Ta(OC₂H₅)₅ as three kinds oforganometallic complexes) and THF (tetrahydrofuran) as a solvent arestored, a gas feed pipe 18 connected to the gas cylinder 11 and thevaporizer 1, an oxygen feed pipe 19 connected to the oxygen cylinder 12and the vaporizer 1, a water feed pipe 20 and a water distribution pipe21, which are connected to the water storage tank 13 and the vaporizer1, liquid feed pipes 22 to 25 which are connected to the reservoirs 14to 17 and the vaporizer 1, and a manifold 26 connected to the reservoirs14 to 17 and the gas cylinder 11.

In the path of the gas feed pipe 18 are provided a valve 18 a and a massflow controller 18 b, in the path of the oxygen feed pipe 19 areprovided a valve 19 a, a mass flow controller 19 b, and a valve 19 c, inthe path of the water feed pipe 20 is provided a valve 20 a, in the pathof the liquid feed pipe 22 for solvent are provided a valve 22 a and amass flow controller 22 b, in the paths of the liquid feed pipes 23 to25 for complex are provided valves 23 a to 25 a and mass flowcontrollers 23 a to 25 b, respectively, and in the path of the manifold26 are provided valves 26 a to 26 d, an air purge 26 e, and a valve 26f. The liquid feed pipes 23 to 25 are branched so as to be connected tothe liquid feed pipe 22, and are provided with valves 23 c to 25 c,respectively.

The carrier gas filled in the gas cylinder 11 is supplied to thevaporizer 1 while the flow rate thereof is controlled by the mass flowcontroller 18 b by opening the valve 18 a of the gas feed pipe 18. Also,the carrier gas filled in the gas cylinder 11 is set into the reservoirs14 to 17 by opening the valve 26 f and the valves 26 a to 26 d of themanifold 26 and by closing the release state of the air purge valve 26e. Thereby, the interiors of the reservoirs 14 to 17 are pressurized bythe carrier gas, and the stored source solutions are pushed up in theliquid feed pipes 22 to 25 the tip end of which are put in thesolutions, and are transported into connection pipes 2 to 5 of thevaporizer 1 after the flow rates thereof have been controlled by themass flow controllers 22 b to 25 b.

Also, at the same time, the oxygen (oxidizing agent), the flow rate ofwhich is controlled to a fixed value by the mass flow controller 19 b,is transported from the oxygen cylinder 12 to the vaporizer 1.

Further, by opening the valve 20 a of the water feed pipe 20, thecooling water in the water storage tank 13 circulates in the vaporizer 1to cool the vaporizer 1.

In the illustrated example, connection pipes 27 to 30 are provided sideby side along the axis line direction of the vaporizer 1. Actually,however, the connection pipes 27 to 30 are provided radially andalternately by connection pipes 31 and 32 connected to the water feedpipe 20 or the water distribution pipe 21 leading to the water storagetank 13.

The source solution stored in the reservoirs 14 to 16 is a solution inwhich a liquid or solid organometallic complex (Sr(DPM)₂, Bi(C₆H₅)₃,Ta(OC₂H₅)₅) is dissolved in THF, which is a solvent, at ordinarytemperature. Therefore, if the source solution is allowed to stand as itis, the organometallic complex is deposited by the evaporation of THFsolvent, and finally becomes in a solid state. For this reason, in orderto prevent the interiors of the liquid feed pipes 23 to 25 that comeinto contact with the source solution from being clogged by thesolid-state organometallic complex, the interiors of the liquid feedpipes 23 to 25 and the interior of the vaporizer 1 should be cleaned byTHF in the reservoir 17 after the film forming work has been finished.At this time, the cleaning operation is performed in a section from theoutlet side of the mass flow controller 23 b to 25 b to the vaporizer 1,and the THF stored in the reservoir 17 is washed away after the work hasbeen finished.

FIG. 3 is a sectional view showing a construction of an essentialportion of the vaporizer 1. In FIG. 3, the vaporizer 1 includes adisperser 2 to which the gas feed pipe 18 is connected, a reaction tube3 connected continuously to the downstream side of the disperser 2, anda heater 4 covering the periphery of the reaction tube 3.

The disperser 2 has a gas passage 5 located coaxially with the gas feedpipe 18. Between a start end upstream port 5 a and a terminus endinjection port 5 b of the gas passage 5, the tip ends of the connectionpipes 27 to 30 are located (in FIG. 3, only the opposedly arrangedconnection pipes 28 and 29 are shown). Thereby, the source solutionsstored in the reservoirs 14 to 16 can be supplied into the gas passage5. Also, the disperser 2 is formed with a cooling path 6 whichcommunicates with the connection pipes 31 and 32 and in which thecooling water in the water storage tank 13 circulates. Further, thedisperser 2 includes a rod 7 one end of which is located on the upstreamside of the start end upstream port 5 a of the gas feed pipe 18 and theother end of which is located at the position of the terminus endinjection port 5 b, and pins 8 for supporting the other end of the rod7. One end of the rod 7 is held by pins 9 provided near the end portionof the gas feed pipe 18.

As the heater 4, a cylindrical ceramic heater that surrounds the reactortube 3 substantially over the total length thereof or a spiral heater isused.

In the above-described configuration, a hole is penetratingly providedin the disperser 2, and the rod 7 having an outside diameter (4.48 mm)smaller than the inside diameter (4.50 mm) of the hole is embedded so asto be located coaxially with the axis line of the hole. The gas passage5 is formed in a space formed between the disperser 2 and the rod 7. Therod 7 is held in a positioned state by the machine screws 9.

The cross section width of the gas passage 5 is 0.02 mm. At this time,the cross section width of the gas passage 5 is preferably 0.005 to 0.10mm. If the cross section width is narrower than 0.005 mm, fabrication isdifficult to do, and if it exceeds 0.10 mm, a high-pressure carrier gasmust be used to increase the velocity of carrier gas.

From the upstream side of the gas passage 5, the carrier gas isintroduced through the gas feed pipe 18. Since the source solution isdripped in this carrier gas from the tip ends of the connection pipes 27to 30 located in midway portions of the gas passage 5, the sourcesolution is dispersed into the carrier gas passing through the gaspassage 5.

Thereby, the carrier gas into which the source solutions are dispersedis injected from the terminus end injection port 5 b on the downstreamside of the gas passage 5 into the reaction tube 3. The carrier gas,into which the source solutions are dispersed and which flows in thereaction tube 3, is heated and vaporized by the heater 4, and thereafteris sent to a thin-film forming apparatus, not shown.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In the vaporizer 1 configured as described above, the periphery of thereaction tube 3 is covered with the heater 4. Therefore, there ariseproblems in that it is difficult to keep a vaporization path length(reaction time) of carrier gas into which the source solutions aredispersed, which corresponds to the length of the reaction tube 3, long,there is produced a difference in heating temperature due to radiationheat of the heater 4 between a portion near the outer periphery of thereaction tube 3 and a portion near the center thereof, and sufficientvaporization cannot be accomplished without a change in size of thevaporizer 1 depending on the kind, dispersion quantity, etc. of thesource solution.

The present invention has been made to solve the above problems, andaccordingly an object thereof is to provide a vaporizer capable ofkeeping the reaction time of carrier gas long.

Means for Solving the Problems

To achieve the above object, a vaporizer described in claim 1 ischaracterized by including a spiral reaction tube to which a carrier gasinto which a source solution consisting of a liquid or powder isdispersed is supplied from the upstream side, and a heater for heatingand vaporizing the carrier gas into which the source solution isdispersed and which passes through the reaction tube by means ofradiation heat.

A vaporizer described in claim 2 is characterized in that the heater isarranged on the inside of the reaction tube.

Advantages of the Invention

According to the vaporizer in accordance with the present invention, acarrier gas into which a source solution consisting of a liquid orpowder is dispersed is supplied from the upstream side to the spiralreaction tube, and the carrier gas into which the source solution isdispersed and which passes through the reaction tube is vaporized byradiation heat from the heater. Thereby, the path of the reaction tubecan be kept long, and the vaporization of carrier gas is promoted evenlyby radiation heat from the heater because the carrier gas into which thesource solution is dispersed is agitated in the direction crossing thepassing direction by a centrifugal force produced when the carrier gaspasses through the reaction tube.

According to the vaporizer described in claim 2, the arrangement of theheater on the inside of the reaction tube contributes to making thevaporizer small in size.

BEST MODE FOR CARRYING OUT THE INVENTION

A vaporizer in accordance with the present invention, which is used as avaporizer for MOCVD, will now be described with reference to theaccompanying drawings.

FIG. 2 is a system block diagram of a vaporization system for MOCVDhaving the vaporizer in accordance with the present invention, and FIG.1 shows an essential portion of the vaporizer in accordance with thepresent invention, FIG. 1(A) being a front view of the essentialportion, and FIG. 1(B) being a sectional view of a reaction tube.

In FIG. 2, reference numeral 10 denotes a supply section for supplying aplurality of source solutions etc. to a vaporizer 101. Theconfigurations of the supply section 10 and a disperser 2 are the sameas those of the conventional art shown in FIG. 4, so that the detailedexplanation thereof is omitted.

The vaporizer 101 includes a disperser 2 to which a gas feed pipe 18 isconnected, a reaction tube 103 connected continuously to the downstreamside of the disperser 2, and a heater 104 covering the periphery of thereaction tube 103.

The reaction tube 103 has a midway portion formed into a spiral shape.For example, a mechanical separation distance from the disperser 2 to athin-film forming apparatus, not shown, is the same as explained in theconventional art, and therefore the size of equipment of the whole ofvaporization system can be made almost the same. Also, since thereaction tube 103 is formed into a spiral shape, the distance of asubstantial reaction portion of the distance from the disperser 2 to thethin-film forming apparatus, not shown, is kept long.

As the heater 104, a rod-shaped heater such as a ceramic heater isarranged in the center of the spiral portion of the reaction tube 103substantially over the total length of the reaction tube 103. The heater104 may be formed by a spiral tube body located on the inside or on theoutside of the reaction tube 103, or may be formed by the spiral tubebodies located on the inside and outside of the reaction tube 103.

In the above-described configuration, the source solution is drippedfrom the tip ends of the connection pipes 27 to 30 connected to thedispersion section 2, and is dispersed into the carrier gas introducedfrom the gas feed pipe 18.

Thereby, the carrier gas into which the source solutions are dispersedis injected from the downstream side of the dispersion section 2 to thereaction tube 103. The carrier gas into which the source solutions aredispersed and which flows in the reaction tube 103 is heated andvaporized by the heater 104, and thereafter is sent into the thin-filmforming apparatus, not shown.

At this time, since the reaction tube 103 is formed into a spiral shape,as shown in FIG. 1(B), a turbulent flow due to centrifugal force occursin the reaction tube 103 in the direction crossing the conveyancedirection of carrier gas, and therefore a state in which the carrier gasis agitated on the inside and outside of the reaction tube is formed, sothat the carrier gas can be vaporized evenly by radiation heat from theheater 104.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is views showing an essential portion of a vaporizer inaccordance with the present invention, FIG. 1(A) being a front view ofthe essential portion, and FIG. 1(B) being a sectional view of areaction tube;

FIG. 2 is a system block diagram of a vaporization system for MOCVDhaving a vaporizer in accordance with the present invention;

FIG. 3 is a longitudinal sectional view of a dispersion section of avaporizer; and

FIG. 4 is a system block diagram of a vaporization system for MOCVDhaving a conventional vaporizer.

EXPLANATION OF SYMBOLS

-   101 . . . vaporizer-   103 . . . reaction tube-   104 . . . heater

INDUSTRIAL APPLICABILITY

According to the vaporizer in accordance with the present invention, acarrier gas into which a source solution consisting of a liquid orpowder is dispersed is supplied from the upstream side to the spiralreaction tube, and the carrier gas into which the source solution isdispersed and which passes through the reaction tube is vaporized byradiation heat from the heater. Thereby, the path of the reaction tubecan be kept long, and the vaporization of carrier gas is promoted evenlyby radiation heat from the heater because the carrier gas into which thesource solution is dispersed is agitated in the direction crossing thepassing direction by a centrifugal force produced when the carrier gaspasses through the reaction tube.

According to the vaporizer described in claim 2, the arrangement of theheater on the inside of the reaction tube contributes to making thevaporizer small in size.

1. A vaporizer characterized by comprising a spiral reaction tube towhich a carrier gas into which a source solution consisting of a liquidor powder is dispersed is supplied from the upstream side, and a heaterfor heating and vaporizing the carrier gas into which the sourcesolution is dispersed and which passes through the reaction tube bymeans of radiation heat.
 2. The vaporizer according to claim 1,characterized in that the heater is arranged on the inside of thereaction tube.